JP2013051028A - Positive electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode for a high capacity nonaqueous electrolyte secondary battery including an active material layer which less likely to peel off from a collector, and to provide a nonaqueous electrolyte secondary battery.SOLUTION: To provide a positive electrode for a nonaqueous electrolyte secondary battery having a long and sheet-like collector, and a first active material layer formed on one surface of the collector, in which the thickness of the first active material layer decreases continuously or gradually in a predetermined direction from one end toward the other end of the collector in the longitudinal direction thereof, the first active material layer contains an active material composed of a complex oxide that contains Li and a transition metal element Me, and the filling rate of the active material in the first active material layer is 85-95%.

Description

  The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery, and more particularly to improvement of an active material layer contained in the positive electrode.

  In recent years, mobile devices such as personal computers and mobile phones are rapidly becoming mobile. As a power source for these electronic devices, a small, light and high capacity secondary battery is required. For these reasons, development of nonaqueous electrolyte secondary batteries capable of increasing the energy density has been widely performed.

  The nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a porous insulating layer interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The positive electrode, the negative electrode, and the porous insulating layer are wound to form an electrode group. The positive electrode includes a sheet-like current collector and an active material layer formed on at least one surface of the current collector.

  On the inner peripheral side of the electrode group, the stress generated in the electrode by winding is large. Therefore, the active material layer is easily cracked or the active material layer is peeled off from the current collector. Therefore, in Patent Documents 1 and 2, the thickness of a part of the active material layer is reduced. It is said that this can relieve the stress caused by winding.

  In Patent Documents 1 and 2, a paste containing an active material is applied to a current collector to form an active material layer on the current collector. In such a paste application method, although the thickness of the active material layer can be easily controlled, there is a limit to the improvement in the filling rate of the active material.

  Therefore, various efforts are being made to improve the filling rate of the active material. For example, in order to increase the filling rate of the active material, it has been proposed to form a dense active material layer by depositing the active material on the current collector surface without using a conductive agent or a binder (patent) References 3 and 4).

JP 2004-303622 A JP 2009-181833 A JP 2007-5219 A JP 2002-29883 A

  In the paste application method as in Patent Documents 1 and 2, in order to increase the filling ratio of the active material, it is important to roll the coating film with a pressure as large as possible. On the other hand, in order to change the thickness of the active material layer continuously or stepwise, it is necessary to change the amount of paste supplied to the current collector and the pressure applied to the coating film continuously or stepwise. However, such control becomes difficult as the rolling pressure increases. For example, it is very difficult to change the thickness of the active material layer because the current collector is torn at a portion where a high pressure is applied. That is, in the paste application method, it is difficult to improve the filling rate of the active material and form an active material layer that does not easily peel off.

  Since the active material layers of Patent Documents 3 and 4 have an active material filling rate that is too high, the flexibility of the electrode is insufficient. Such an active material layer cannot sufficiently relieve stress caused by winding even if the thickness is controlled.

  Accordingly, an object of the present invention is to provide a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that have a high capacity and that an active material layer is unlikely to peel off from a current collector.

  A positive electrode for a non-aqueous electrolyte secondary battery of the present invention has a long and sheet-like current collector, and a first active material layer formed on one surface of the current collector, and the first active material The thickness of the layer decreases continuously or stepwise in a predetermined direction from one end to the other end in the longitudinal direction of the current collector, and the first active material layer includes Li and a transition metal. The active material which consists of complex oxide containing element Me is included, and the filling rate of the active material in a 1st active material layer is 85 to 95%.

  The present invention also includes the above-described positive electrode, negative electrode, a porous insulating layer interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, and the positive electrode, the negative electrode, and the porous insulating layer are wound to form an electrode group. A nonaqueous electrolyte secondary battery is provided in which one end is disposed on the outer peripheral side of the electrode group and the other end is disposed in the center.

  By using the positive electrode of the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that has a high capacity and the active material layer is difficult to peel off from the current collector.

It is sectional drawing which shows roughly the structure of the positive electrode which concerns on one Embodiment of this invention. It is a longitudinal cross-sectional view which shows an example of a film-forming apparatus roughly. 1 is a cross-sectional view schematically showing a cylindrical nonaqueous electrolyte secondary battery.

  The positive electrode of the present invention has a long and sheet-like current collector and a first active material layer formed on one surface of the current collector. The thickness of the first active material layer decreases continuously or stepwise in a predetermined direction from one end to the other end in the longitudinal direction of the current collector. The positive electrode of the present invention is wound together with the negative electrode and the porous insulating layer to constitute an electrode group. At this time, one end of the positive electrode is disposed on the outer peripheral side of the electrode group, and the other end is disposed at the center. That is, the active material layer has the smallest thickness on the winding start side of the electrode group having a small curvature radius, and the first active material layer has the largest thickness on the winding end side having a large curvature radius. At this time, the thickness of the active material layer only needs to decrease on the average from the outer peripheral side to the inner peripheral side of the electrode group, and even if a region where the thickness is locally increased is included. good.

The state in which the thickness of the active material layer is continuously or gradually reduced is, for example, the following state. The current collector is divided into three equal parts in a predetermined direction from one end portion to the other end portion in the longitudinal direction of the current collector, and the thicknesses of three arbitrary points are measured in each region. Thereby, the average thickness of each area | region of an active material layer is calculated | required. The average thickness of the active material layer in the region of one end side is T _1, the average thickness of the active material layer and T ₂ in the central area, the average thickness of the active material layer in the region of the other end Let T ₃ be the size. When T ₁ , T ₂ and T ₃ satisfy T ₁ > T ₂ > T ₃ , it can be said that the thickness of the active material layer decreases continuously or stepwise.

  The stress generated by winding when producing the electrode group is larger on the inner peripheral side than on the outer peripheral side. Therefore, by increasing the thickness of the active material layer on the outer peripheral side and reducing the thickness of the active material layer on the inner peripheral side, it is possible to efficiently relieve the stress caused by winding while maintaining the battery capacity. Can do.

  The average thickness in the vicinity of one end (first end) of the first active material layer is preferably 1.05 to 4 times the average thickness in the vicinity of the other end (second end). 1.1 to 2 times is more preferable. The average thickness in the vicinity of the end portion of the first active material layer may be obtained by, for example, measuring the thickness of any three points in the vicinity of the end portion and obtaining the average. Here, the vicinity of the end portion refers to a region from the end portion to L / 10, where L is a dimension in the longitudinal direction of the active material layer.

  The filling rate of the active material in the first active material layer is 85 to 95%. The active material filling rate is the volume ratio of the active material to the entire active material layer. The higher the filling ratio of the active material, the higher the capacity of the battery can be obtained, but the active material layer tends to crack or peel off. For this reason, the thickness of the active material layer is reduced continuously or stepwise in a predetermined direction from one end to the other end in the longitudinal direction of the current collector, and stress caused by winding is efficiently reduced. It is effective to do. The filling rate of the active material can be obtained by measuring the weight of the active material layer and the thickness of the active material layer, or measuring the thickness of the active material layer and the amount of the active material. The abundance of the active material can be measured by ICP emission spectral analysis or the like. When the filling ratio of the active material is less than 85%, a high capacity positive electrode cannot be obtained. When the filling ratio of the active material exceeds 95%, the flexibility of the electrode becomes insufficient, and the active material layer is likely to be cracked or peeled off.

  The positive electrode of the present invention preferably further has a second active material layer formed on the other surface of the current collector. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a positive electrode according to an embodiment of the present invention. 1 includes a sheet-like current collector 20, a first active material layer 21 formed on one surface of the current collector, and a second active material formed on the other surface of the current collector. Layer 22.

  Similar to the first active material layer, the thickness of the second active material layer decreases continuously or stepwise in a predetermined direction from one end to the other end in the longitudinal direction of the current collector. Preferably it is. Also in the second active material layer, the average thickness in the vicinity of one end corresponding to the first end 23 of the first active material layer is the average thickness in the vicinity of the other end corresponding to the second end 24. It is preferably 1.1 to 3 times, and more preferably 1.1 to 2 times. What is necessary is just to obtain | require the average thickness of the edge part of a 2nd active material layer similarly to a 1st active material layer. The filling rate of the active material in the second active material layer is preferably 85 to 95%, similarly to the first active material layer.

  The average thickness of the first active material layer is preferably smaller than the average thickness of the second active material layer. At this time, a region where the thickness of the first active material layer is locally larger than the thickness of the second active material layer may be included. In the electrode group, the first active material layer is disposed on the inner side, and the second active material layer is disposed on the outer side.

The average thickness of the first active material layer is preferably 0.7 to 0.95 times, more preferably 0.85 to 0.95 times the average thickness of the second active material layer.
The average thickness of the active material layer may be determined, for example, by measuring the thickness of any three points near both ends in the longitudinal direction and the thickness of any three points near the center. Here, the vicinity of the center means a region from the center in the longitudinal direction to L / 10 on the left and right.

The structure of the active material layer is not particularly limited. It may be a homogeneous film or may have a structure containing active material particles such as a columnar or dendritic shape.
In a preferred embodiment of the present invention, the active material forms a deposited film that does not contain a binder. Thereby, the filling rate of the active material can be improved. The binder is made of a resin component and does not contribute to the charge / discharge capacity. Therefore, a non-aqueous electrolyte secondary battery with a higher capacity can be obtained by forming a deposited film that does not contain a binder.

  The deposited film preferably contains dendritic active material particles. The dendritic active material particles are branched into a plurality of branches from the bottom on the current collector side toward the surface of the deposited film.

  By including the dendritic active material particles in the deposited film, the specific surface area of the active material layer is increased, so that the area where the active material layer and the nonaqueous electrolyte are in contact with each other is increased. Thereby, the positive electrode for nonaqueous electrolyte secondary batteries which has a favorable charging / discharging characteristic by especially a high current density is obtained.

  In the dendritic active material particles, the bottom is bonded to the current collector. As the dendritic active material particles go to the bottom, branching decreases, and the contact area between the current collector and the dendritic active material particles increases. Therefore, the electronic resistance between the current collector and the active material layer is reduced. The number of branches increases as it goes to the surface side of the active material layer.

  When the active material layer includes dendritic active material particles, the active material layer has excellent flexibility, and thus the active material layer is unlikely to peel off from the current collector even when wound. When the active material layer of the present invention includes dendritic active material particles, the stress caused by winding can be sufficiently relaxed, and the active material layer is more difficult to peel off from the current collector.

  In addition to the dendritic shape, the dendritic active material particles include, for example, active material particles such as a cage shape, a tuft shape, and a broccoli shape.

  The active material layer preferably includes a polymer gel having ion conductivity between the dendritic active material particles. Thereby, damage to the active material particles due to external stress and peeling of the active material layer can be suppressed.

  The polymer gel includes a non-aqueous electrolyte, a conductive aid, and a polymer that holds them. When the polymer gel retains the non-aqueous electrolyte, ion conductivity is exhibited, and charge / discharge characteristics at a high current density are further improved. Moreover, peeling of the active material layer derived from the stress caused by winding or the volume expansion of the active material accompanying charging / discharging can be suppressed more favorably.

  For example, the polymer gel can be included in the active material layer by applying a polymer gel on the surface of the active material layer or immersing the positive electrode on which the active material layer is formed in the polymer gel.

  A method for manufacturing the first active material layer and the second active material layer is not particularly limited, but it is preferable to form a deposited film by a thermal plasma method. According to the thermal plasma method, the filling rate of the active material can be increased to 90% or more, and an appropriate void can be formed in the active material layer.

An example of a film forming apparatus using thermal plasma will be described with reference to the drawings.
FIG. 2 is a cross-sectional view schematically showing an example of a film forming apparatus. The film forming apparatus includes a chamber 1 that provides a space for film formation and a thermal plasma generation source. The thermal plasma generation source includes a torch 10 that provides a space for generating thermal plasma, and an induction coil 2 that surrounds the torch 10. A power source 9 is connected to the induction coil 2.

  The chamber 1 may or may not include the exhaust pump 5 as necessary. By removing the air remaining in the chamber 1 with the exhaust pump 5 and then generating thermal plasma, contamination of the active material can be suppressed. By using the exhaust pump 5, the shape of the plasma gas flow can be easily controlled. Furthermore, it becomes easy to control the film forming conditions such as the pressure in the chamber 1. The chamber 1 may include a filter (not shown) for collecting dust.

  A stage 3 is installed vertically below the torch 10. Although the material of the stage 3 is not specifically limited, It is preferable that it is excellent in heat resistance, for example, stainless steel etc. are mentioned. A current collector 4 is disposed on the stage 3. The stage 3 may have a cooling unit (not shown) that cools the current collector as necessary. The stage 3 may be a roll. In this case, by continuously forming the film on the surface of the current collector while changing the rotation speed of the roll, the thickness is continuously increased in a predetermined direction from one end to the other end in the longitudinal direction of the current collector. A small active material layer can be easily formed.

  One end of the torch 10 is released to the chamber 1 side. The torch 10 is preferably made of, for example, ceramics (quartz or silicon nitride). By increasing the inner diameter of the torch, the reaction field can be made wider. Therefore, an active material layer can be formed efficiently.

  A gas supply port 11 and a raw material supply port 12 are arranged at the other end of the torch 10. The gas supply port 11 is connected to gas supply sources 6a and 6b via valves 7a and 7b. The raw material supply port 12 is connected to the raw material supply source 8. By supplying gas from the gas supply port 11 to the torch 10, thermal plasma can be generated efficiently.

  From the viewpoint of stabilizing the thermal plasma and controlling the gas flow in the thermal plasma, a plurality of gas supply ports 11 may be provided. When a plurality of gas supply ports 11 are provided, the direction in which the gas is introduced is not particularly limited, and may be the axial direction of the torch 10, a direction perpendicular to the axial direction of the torch 10, or the like. As the amount of gas introduced from the axial direction of the torch 10 increases, the gas flow in the thermal plasma becomes thinner and the central portion of the gas flow becomes higher temperature, so that the raw material is easily vaporized and decomposed. From the viewpoint of stabilizing the thermal plasma, it is preferable to control the gas introduction amount using a mass flow controller (not shown) or the like.

  When a voltage is applied from the power source 9 to the induction coil 2, thermal plasma is generated in the torch 10. The voltage to be applied may be a high frequency voltage or a DC voltage. Alternatively, a high frequency voltage and a DC voltage may be used in combination.

  When the thermal plasma is generated, the induction coil 2 and the torch 10 become high temperature. Therefore, it is preferable to provide a cooling unit (not shown) around the induction coil 2 and the torch 10. For example, a water-cooled cooling device or the like may be used as the cooling unit.

Using the above apparatus, the first active material layer and the second active material layer can be formed as follows.
First, thermal plasma is generated. The thermal plasma is preferably generated in an atmosphere containing at least one gas selected from the group consisting of argon, helium, oxygen, hydrogen and nitrogen. From the viewpoint of generating thermal plasma stably and efficiently, it is more preferable to generate thermal plasma in an atmosphere containing diatomic molecules such as hydrogen. When a reactive gas such as oxygen, hydrogen, nitrogen, or an organic gas is used in combination with an inert gas such as a rare gas, an active material is generated using the reaction between the raw material and the reactive gas. Also good.

  When using a high-frequency electromagnetic field, the thermal plasma is generated by applying a high frequency to the coil by an RF power source. At this time, the frequency of the power supply is preferably 1000 Hz or more, for example, 13.56 MHz.

  When the film forming apparatus as shown in FIG. 2 is used, the injection speed of the gas discharged from the gas supply port is slower than the case of generating plasma by DC arc discharge (several thousand m / s), about several tens to 100 m / s. For example, it can be 900 m / s or less. Thereby, the time for which the raw material stays in the thermal plasma can be made relatively long, and the raw material can be sufficiently dissolved, vaporized or decomposed in the thermal plasma. Therefore, it is possible to efficiently synthesize the active material and form a film on the current collector.

  Next, the raw material for the active material layer is supplied into the thermal plasma. Thereby, the particle | grains used as the precursor of an active material in a thermal plasma are produced | generated. When a plurality of raw materials are used, the respective raw materials may be separately supplied into the thermal plasma, but it is preferable to supply the raw plasma after sufficiently mixing the raw materials.

  Particles generated in the thermal plasma are supplied from a substantially normal direction of the surface of the current collector and are deposited on the current collector to form a positive electrode active material layer. For example, the thickness of the active material layer can be reduced continuously or stepwise in a predetermined direction from one end to the other end in the longitudinal direction of the current collector as follows. In the sheet-like current collector, the surface on which the active material layer is formed is divided into a plurality of regions having an arbitrary size, and active material layers having different thicknesses are formed in the respective regions. Thereby, the thickness of the active material layer can be reduced stepwise in a predetermined direction from one end to the other end in the longitudinal direction of the current collector. The region other than the region where the active material layer is formed may be covered with a shielding object such as a mask. The thickness of the active material layer can be changed in each region, for example, by controlling the film formation time and the supply rate of the raw material into the thermal plasma.

  In addition, when the stage 3 is a roll, the active material layer may be formed on the current collector surface while sequentially changing the rotation speed of the roll. Also by this method, the thickness of the active material layer can be reduced continuously or stepwise in a predetermined direction from one end to the other end in the longitudinal direction of the current collector.

  The raw material supplied into the thermal plasma may be in a liquid state or a powder state. However, it is easier to supply the raw material in the thermal plasma in a powder state, which is advantageous in terms of manufacturing cost. The raw material in the powder state is also relatively cheaper than the raw material in the liquid state (for example, alkoxide).

  When the raw material is supplied in the thermal plasma in a liquid state, it may be necessary to remove impurities such as a solvent and carbon. On the other hand, when supplying a raw material in a thermal plasma in a powder state, since the impurities as described above are hardly contained, a positive electrode having excellent electrochemical characteristics can be obtained.

  When supplying a raw material in a thermal plasma in a powder state, the D50 (volume-based median diameter) of the raw material is preferably less than 20 μm. When the median diameter of the raw material exceeds 20 μm, the raw material may not be sufficiently vaporized or decomposed in the thermal plasma, and it may be difficult to generate an active material.

The supply rate of the raw material into the thermal plasma varies depending on the volume of the apparatus, the temperature of the plasma, etc., but is, for example, 0.0002 to 0.05 g / min per kilowatt output of the high frequency voltage applied to the induction coil. preferable.
When the feed rate of the raw material into the thermal plasma exceeds 0.05 g / min per 1 kilowatt of the high frequency voltage applied to the induction coil, the adhesion with the current collector may be lowered.

  The structure of the active material layer can be controlled by the supply rate of the raw material into the thermal plasma. Therefore, the relationship between the supply rate of the raw material into the thermal plasma and the structure of the active material layer is preferably obtained in advance as information. An active material layer having a desired structure can be formed by controlling the supply rate of the raw material into the thermal plasma based on the obtained information.

  Various materials can be used as the raw material of the active material. For example, (i) a raw material containing a lithium compound and a compound containing a transition metal element Me, (ii) a raw material containing a composite oxide containing Li and the transition metal element Me, or the like is used.

  Examples of the lithium compound include lithium oxide, lithium hydroxide, lithium carbonate, and lithium nitrate. These may be used alone or in combination of two or more.

  Examples of the compound containing the transition metal element Me include nickel compounds, cobalt compounds, manganese compounds, and iron compounds. These may be used alone or in combination of two or more. Examples of the nickel compound include nickel oxide, nickel carbonate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide, and the like. Examples of the cobalt compound include cobalt oxide, cobalt carbonate, cobalt nitrate, and cobalt hydroxide. Examples of the manganese compound include manganese oxide and manganese carbonate. Examples of the iron compound include iron oxide and iron carbonate.

  For example, in the case of forming a positive electrode active material layer containing a composite oxide, a lithium compound and a compound containing a transition metal are supplied into thermal plasma as raw materials for the active material. These compounds may be supplied separately into the thermal plasma, but it is preferable to supply them to the thermal plasma after sufficient mixing.

  Since lithium is easily evaporated in the thermal plasma, the mixing ratio of the lithium compound in the raw material is preferably larger than the stoichiometric ratio of lithium in the target active material.

  A composite oxide (active material itself) containing Li and the transition metal element Me can also be used as a raw material. The composite oxide containing Li and the transition metal element Me supplied into the thermal plasma is dissolved, vaporized, decomposed, re-synthesized, and deposited on the current collector.

The positive electrode active material layer of the present invention includes a positive electrode active material made of a composite oxide containing Li and a transition metal element Me (hereinafter also simply referred to as a composite oxide). The composite oxide preferably has a layered or hexagonal crystal structure or a spinel structure. Examples of the transition metal element Me include Co, Ni, Mn, Fe, and the like. Specifically, LiCoO ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiNi _1/2 Co _1/2 O ₂ , LiNiO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiNi _{1 / 2} Fe _1/2 O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , Li _4/3 Ti _5/3 O _{4 and the} like. Further, the composite oxide may contain Al. The complex oxide containing Al is Li _x Me _y Al _1-y O _{1 + a} (Me is at least one selected from the group consisting of Co, Ni, Mn, and Fe, and 0.9 ≦ x ≦ 1 .5, 0.01 ≦ y ≦ 0.3, 0 ≦ a ≦ 0.2) and the like. Only one type of positive electrode active material may be used alone, or two or more types may be used in combination.

The positive electrode current collector is not particularly limited, and for example, a conductive material generally used in an electrochemical element can be used. Specifically, it is desirable to use Al, Ti, stainless steel (SUS), Au, Pt, or the like. These current collectors are preferable in that the elution of metal from the current collector is relatively small even when the Li desorption reaction is performed to about 3.5 to 4.5 V (vs. Li / Li ⁺ ).

The nonaqueous electrolyte secondary battery of the present invention will be described.
The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a porous insulating layer interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, and the positive electrode, the negative electrode, and the porous insulating layer are wound. To constitute an electrode group. The non-aqueous electrolyte secondary battery of the present invention includes the positive electrode for a non-aqueous electrolyte secondary battery described above, and other configurations are not particularly limited.

  In the non-aqueous electrolyte secondary battery, one end of the current collector is disposed on the outer peripheral side of the electrode group, and the other end is disposed in the center. That is, the active material layer has the smallest thickness on the winding start side of the electrode group having a small curvature radius, and the first active material layer has the largest thickness on the winding end side having a large curvature radius. . On the winding end side with a large radius of curvature, the active material layer is unlikely to peel off from the current collector during winding even if it does not contain a binder. Therefore, it is possible to increase the thickness of the active material layer toward the winding end side having a large curvature radius. According to the present invention, it is possible to increase the capacity while suppressing the peeling of the active material layer.

  The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The porous insulating layer is impregnated with a nonaqueous electrolyte. The case that accommodates the positive electrode, the negative electrode, and the porous insulating layer and the sealing plate are insulated from each other by a gasket.

As the negative electrode active material, a carbon material, a metal, an alloy, a metal oxide, a metal nitride, or the like is used. As the carbon material, natural graphite, artificial graphite and the like are preferable. As the metal or alloy, lithium alone, lithium alloy, silicon alone, silicon alloy, tin alone, tin alloy and the like are preferable. The metal oxide is preferably SiO _x (0 <x <2, preferably 0.1 ≦ x ≦ 1.2).

  As the current collector for the negative electrode, it is desirable to use Cu, Ni, SUS or the like.

  For the porous insulating layer, for example, a nonwoven fabric or a microporous film made of polyethylene, polypropylene, aramid resin, amideimide, polyphenylene sulfide, polyimide, or the like can be used. The nonwoven fabric or microporous film may be a single layer or a multilayer structure. The inside or the surface of the porous insulating layer may contain a heat resistant filler such as alumina, magnesia, silica, titania.

The non-aqueous electrolyte includes a non-aqueous solvent and a solute dissolved in the non-aqueous solvent. The solute is not particularly limited, and may be appropriately selected in consideration of the redox potential of the active material. Preferred solutes include LiPF ₆ and LiBF ₄ .

  The non-aqueous solvent is not particularly limited. For example, ethylene carbonate (EC), propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate (EMC), or the like may be used. These may be used alone or in combination of two or more.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. These examples and comparative examples do not limit the present invention.
Example 1
(i) Production of Positive Electrode As a film forming apparatus, a high frequency induction thermal plasma generator (TP-12010) manufactured by JEOL Ltd. having a chamber with an internal volume of 6250 cm ³ and a thermal plasma generation source was used. As the thermal plasma generation source, a torch made of a silicon nitride tube having a diameter of 42 mm and a copper induction coil surrounding the torch were used.

A sheet-like current collector (5 × 20 cm, thickness 20 μm) containing Al was placed on the stage. Thereafter, the air in the chamber was replaced with argon gas.
Argon gas was introduced into the chamber at a flow rate of 50 L / min, and oxygen gas was introduced at a flow rate of 30 L / min. The pressure in the chamber was 18 kPa. A high frequency voltage of 42 kW and a frequency of 3.5 MHz was applied to the induction coil to generate thermal plasma.

As a raw material, a mixture of Li ₂ O and Co ₃ O ₄ was used. Li ₂ O was classified to 30 μm or less. The average particle diameter D50 (based on volume) of Co ₃ O ₄ was 5 μm. Li ₂ O and Co ₃ O ₄ were mixed so that the stoichiometric ratio was Li: Co = 1.3: 1. Argon gas was introduced into one flow path at 50 L / min and oxygen gas at 30 L / min, and these mixed gases were introduced into the chamber from two directions. Here, the ratio of the gas introduction amount from the axial direction of the torch and the gas introduction amount from the direction substantially perpendicular to the axial direction of the torch (hereinafter referred to as D _x : D _y ) was set to 35:45.

  The active material layer A was formed by dividing one surface of the current collector into first to fourth regions each having a size of about 5 × 5 cm. The supply rate of the raw material into the thermal plasma was 0.10 g / min. First, a film is formed for 300 minutes in a region (fourth region) on the other end (second end) side in a predetermined direction from one end in the longitudinal direction of the current collector to the other end. A film having a thickness of 15 μm was formed. Next, a film was formed for 450 minutes in a region (third region) adjacent to the fourth region to form a film having a thickness of 22 μm. Further, a film was formed for 680 minutes in a region adjacent to the third region (second region) to form a film having a thickness of 33 μm. Finally, a film was formed for 1015 minutes in a region (first region) adjacent to the second region on one end (first end) side to form a film having a thickness of 50 μm. Thus, an active material layer A having a thickness that gradually decreases in a predetermined direction from one end portion to the other end portion in the longitudinal direction of the current collector was formed. Note that the thickness of the active material layer A was measured at three points for each region, and the average was obtained.

  Thereafter, the other surface of the current collector was divided into a first region to a fourth region in the same manner as described above, and an active material layer B was formed. The supply rate of the raw material into the thermal plasma was set to 0.10 g / min similarly to the second active material layer. The temperature in the vicinity of the current collector during film formation was about 500 ° C. First, a film having a thickness of 10 μm was formed in a fourth region corresponding to the fourth region of the active material layer A for 200 minutes. A film having a thickness of 15 μm was formed in the third region corresponding to the third region of the active material layer A for 300 minutes. Furthermore, a film having a thickness of 22 μm was formed in the second region corresponding to the second region of the active material layer A for 450 minutes. Finally, a film having a thickness of 33 μm was formed in a first region corresponding to the first region of the active material layer A for 675 minutes. As a result, an active material layer B having a thickness gradually reduced in a predetermined direction from one end portion to the other end portion in the longitudinal direction of the current collector was formed. The thickness of the active material layer B was determined in the same manner as the active material layer A. In the above, the active material layer A corresponds to the second active material layer, and the active material layer B corresponds to the first active material layer.

It was confirmed by X-ray diffraction measurement that an active material layer containing LiCoO ₂ was formed in Example 1.

  When the filling rate of the active material in the positive electrode was determined from the thickness and weight of the active material layer, it was 90%. Thereafter, the positive electrode was cut to a width that can be accommodated in a cylindrical battery case.

[Evaluation of cracking and peeling of active material layer]
The produced positive electrode was wound around a SUS core having a diameter of 5 mm. Winding was started from the end of the positive electrode on the fourth region side, and wound so that the end of the first region side was arranged on the outer peripheral side. When the positive electrode was confirmed, no cracking or peeling of the active material layer was confirmed.

(ii) Preparation of negative electrode 150 parts by weight of graphite as a negative electrode active material, 9 parts by weight of SBR as a negative electrode binder, 1.5 parts by weight of CMC as a thickener, and an appropriate amount of water The mixture was mixed to prepare a negative electrode mixture paste.

  A negative electrode agent paste was applied to both sides of a copper foil having a thickness of 8 μm, which was a negative electrode current collector, and dried. The dried coating film was rolled with a roller to produce a negative electrode having a sheet-like current collector and a negative electrode active material layer. Both sides of the total thickness of the current collector and the negative electrode active material layer (negative electrode thickness) were 190 μm. Thereafter, the negative electrode was cut to a width that could be accommodated in a cylindrical battery case.

(Iii) Preparation of non-aqueous electrolyte A non-aqueous electrolyte was prepared by dissolving LiPF ₆ as a solute at a concentration of 1.25 mol / L in a non-aqueous solvent. The non-aqueous solvent is a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1: 1: 8, and 4% by volume of vinylene carbonate (VC) as an additive. What was added was used.

(Iv) Production of Nonaqueous Electrolyte Secondary Battery A cylindrical nonaqueous electrolyte secondary battery shown in FIG. 3 was produced by the following procedure.
One end of an aluminum positive electrode lead 35 a was connected to the current collector of the positive electrode 35. One end of a copper negative electrode lead 36 a was connected to the current collector of the negative electrode 36.
The positive electrode 35 and the negative electrode 36 were wound through a separator 37 between them to produce a columnar electrode group. At this time, one end of the current collector of the positive electrode 35 was arranged on the outer peripheral side of the electrode group, and the other end was arranged in the center. In the electrode group, the first active material layer was disposed on the inner side, and the second active material layer was disposed on the outer side.

  Both end surfaces of the obtained electrode group were sandwiched between an upper insulating plate 38a and a lower insulating plate 38b and accommodated in a cylindrical battery case 31 having a predetermined size. The other end of the negative electrode lead 36 a was connected to the inner bottom surface of the battery case 31. Thereafter, 5 g of the nonaqueous electrolyte was poured into the battery case 31, and the electrode group was impregnated with the nonaqueous electrolyte under reduced pressure.

Thereafter, the other end of the positive electrode lead 35 a was connected to the lower surface of the sealing body 32.
The end of the opening of the battery case 31 was caulked to the sealing body 32 via the gasket 33. Thereby, a cylindrical nonaqueous electrolyte secondary battery having a design capacity of 337 mAh was produced.

Example 2
N-methyl-2-pyrrolidone (NMP), polyvinylidene fluoride (PVDF, # 7200 manufactured by Kureha Co., Ltd.) and acetylene black were mixed at a weight ratio of 2: 98: 2 to obtain a resin solution (hereinafter referred to as No. 1). Also referred to as a one-layer solution).

In a mixed solvent containing EC, EMC, and diethyl carbonate (DEC) in a volume ratio of 2: 3: 5, LiPF ₆ as a solute is dissolved at a concentration of 1.25 mol / L, and a liquid non-aqueous electrolyte is obtained. Prepared. This liquid non-aqueous electrolyte, PVDF (# 8500 manufactured by Kureha Co., Ltd.), and dimethyl carbonate (DMC) are mixed at a weight ratio of 3:45:52 to obtain a resin solution (hereinafter, second layer solution). (Also called).

  A positive electrode similar to that of Example 1 was immersed in the first layer solution for 10 seconds, and the positive electrode was impregnated with the first layer solution, and then dried at 80 ° C. for 15 minutes. Then, it was immersed in the 2nd layer solution, and the polymer gel was included in the active material layer. This produced the positive electrode of Example 2.

  When the produced positive electrode was evaluated in the same manner as in Example 1, no cracking or peeling of the active material layer was confirmed.

  A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the above positive electrode was used.

《Reference example》
Both surfaces of the current collector were formed in the same manner as in the winding outside of Example 1. When the electrode plate was wound around the winding core in the same manner as in Example 1, the active material was peeled off on the winding start side. Therefore, a cylindrical battery could not be manufactured.

<< Comparative Example 1 >>
An active material layer A having a thickness of 22 μm was formed on almost the entire surface of one side of a sheet-like current collector similar to that of Example 1 for 1320 minutes at the same feed rate as in Example 1. Thereafter, a film was formed for almost 1320 minutes at the same raw material supply rate as in Example 1 over almost the entire opposite surface of the current collector to form an active material layer B having a thickness of 22 μm. Thereby, the positive electrode of Comparative Example 1 was produced.
The thicknesses of the active material layers A and B of Comparative Example 1 hardly changed in a predetermined direction from one end portion to the other end portion in the longitudinal direction of the current collector. When the produced positive electrode was evaluated in the same manner as in Example 1, the active material layer was peeled off from the current collector. Therefore, a cylindrical battery could not be manufactured.

<< Comparative Example 2 >>
A current collector (thickness 1 mm) made of an Au plate was placed on the stage, and an active material layer was formed on the current collector using a magnetron sputtering apparatus. LiCoO ₂ was used as a target. The target diameter was 3 inches. The distance between the current collector on the stage and the target was 3.5 cm.

The degree of vacuum in the chamber was set to 5 × 10 ⁻² Pa using a rotary pump and a diffusion pump. Thereafter, argon gas was introduced into the chamber at a flow rate of 8 × 10 ⁻² L / min and oxygen gas was introduced at a flow rate of 2 × 10 ⁻² L / min so that the degree of vacuum in the chamber was 1 Pa. A high frequency voltage of 80 W and a frequency of 13.56 MHz was applied to the target to generate plasma.

  The temperature in the vicinity of the current collector was set to 300 ° C., and one surface of the current collector was divided into first to fourth regions each having a size of about 5 × 5 cm, and the active material layer A was formed. . First, a film is formed for 900 minutes on a region (fourth region) on the other end (second end) side in a predetermined direction from one end in the longitudinal direction of the current collector to the other end. A film having a thickness of 15 μm was formed. Next, a film was formed for 1320 minutes in a region (third region) adjacent to the fourth region to form a film having a thickness of 22 μm. Further, a film was formed in a region adjacent to the third region (second region) for 1980 minutes to form a film having a thickness of 33 μm. Finally, film formation was performed for 3000 minutes on a region (first region) adjacent to the second region on one end (first end) side to form a film having a thickness of 50 μm. Thus, an active material layer A having a thickness that gradually decreases in a predetermined direction from one end portion to the other end portion in the longitudinal direction of the current collector was formed.

Thereafter, the other surface of the current collector was divided into a first region to a fourth region in the same manner as described above, and an active material layer B was formed. The temperature in the vicinity of the current collector during film formation was about 300 ° C. First, a film having a thickness of 10 μm was formed in a fourth region corresponding to the fourth region of the active material layer A for 600 minutes. A film having a thickness of 15 μm was formed in the third region corresponding to the third region of the active material layer A for 900 minutes. Furthermore, a film having a thickness of 22 μm was formed in the second region corresponding to the second region of the active material layer A for 450 minutes. Finally, a film having a thickness of 33 μm was formed in the first region corresponding to the first region of the active material layer for 675 minutes. Thus, an active material layer B having a thickness that gradually decreases in a predetermined direction from one end portion to the other end portion in the longitudinal direction of the current collector was formed. In the above, the active material layer A corresponds to the second active material layer, and the active material layer B corresponds to the first active material layer. Then baked 1 hour at 500 ° C., to improve the crystallinity of LiCoO _2, to produce a positive electrode.

When ICP analysis was performed on the active material layer, it was confirmed that the element ratio in the active material layer was Li: Co = 0.98: 1.
A cylindrical battery was produced in the same manner as in Example 1 except that the above positive electrode was used.

[Battery evaluation]
The batteries of Examples 1 and 2 and Comparative Example 2 were charged and discharged for 20 cycles in the range of 3.05 to 4.25 V with respect to Li / Li ⁺ , and the initial discharge capacity of 0.2C and the 20th cycle The discharge capacity was measured. The temperature condition was 20 ° C. The results are shown in Table 1.

  After charging / discharging, the batteries of the examples and comparative examples were disassembled, the electrode group was taken out, and the presence or absence of peeling of the positive electrode was confirmed. In both Example 1 and Example 2, no cracking or peeling of the active material layer was confirmed.

  On the other hand, in the battery of Comparative Example 2, the active material layer was peeled off from the current collector. The active material layer formed by sputtering has an excessively high filling rate of the active material. Therefore, the flexibility of the electrode becomes insufficient, the expansion and contraction associated with charge / discharge cannot be relieved, and the active material layer is considered to have peeled from the current collector.

Compared to Comparative Example 3, in Examples 1 and 2, the discharge capacity at the 20th cycle was large.
In Comparative Example 3, it is considered that the active material was densely formed, so that the active material layer was peeled off from the current collector without being able to withstand the expansion and contraction associated with charge and discharge, and the capacity was greatly reduced. In Example 2 in which the active material layer contains a polymer gel, the discharge capacity at the 20th cycle was further improved than in Example 1.

  From the above, it was found that the positive electrode for a non-aqueous electrolyte secondary battery of the present invention has a high capacity and the active material layer is difficult to peel off from the current collector.

  According to the present invention, it is possible to provide a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that have a high capacity and in particular the active material layer is difficult to peel off from the current collector. The nonaqueous electrolyte secondary battery of the present invention is useful as a power source for small electronic devices such as mobile phones and large electronic devices.

DESCRIPTION OF SYMBOLS 1 Chamber 2 Induction coil 3 Stage 4 Current collector 5 Exhaust pump 6a, 6b Gas supply source 7a, 7b Valve 8 Raw material supply source 9 Power supply 10 Torch 11 Gas supply port 12 Raw material supply port 20 Current collector 21 First active material layer 22 Second Active Material Layer 23 First End 24 Second End 31 Battery Case 32 Sealing Body 33 Gasket 35 Positive Electrode 35a Positive Electrode Lead 36 Negative Electrode 36a Negative Electrode Lead 37 Separator 38a Upper Insulating Plate 38b Lower Insulating Plate

Claims (9)

A long and sheet-like current collector, and a first active material layer formed on one surface of the current collector,
The thickness of the first active material layer is reduced continuously or stepwise in a predetermined direction from one end to the other end in the longitudinal direction of the current collector,
The first active material layer includes an active material composed of a composite oxide containing Li and a transition metal element Me;
The positive electrode for nonaqueous electrolyte secondary batteries whose filling rate of the said active material in a said 1st active material layer is 85 to 95%. A second active material layer formed on the other surface of the current collector,
A thickness of the second active material layer is reduced continuously or stepwise in the predetermined direction;
The second active material layer includes an active material made of a composite oxide containing Li and a transition metal element Me;
The positive electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein a filling rate of the active material in the second active material layer is 85 to 95%.   The positive electrode for a nonaqueous electrolyte secondary battery according to claim 2, wherein an average thickness of the first active material layer is smaller than an average thickness of the second active material layer.   The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the active material forms a deposited film that does not contain a binder.   The deposited film includes dendritic active material particles, and the dendritic active material particles are branched into a plurality of branches from the bottom on the current collector side toward the surface side of the deposited film. The positive electrode for nonaqueous electrolyte secondary batteries of Claim 4.   The non-aqueous solution according to claim 5, further comprising a polymer gel having ion conductivity between the dendritic active material particles, wherein the polymer gel includes a non-aqueous electrolyte, a conductive additive, and a polymer holding them. Positive electrode for electrolyte secondary battery. Comprising a positive electrode, a negative electrode, a porous insulating layer interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte;
The positive electrode, the negative electrode, and the porous insulating layer are wound to form an electrode group,
The positive electrode according to claim 1,
The non-aqueous electrolyte secondary battery, wherein the one end is disposed on the outer peripheral side of the electrode group, and the other end is disposed in the center. Comprising a positive electrode, a negative electrode, a porous insulating layer interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte;
The positive electrode, the negative electrode, and the porous insulating layer are wound to form an electrode group,
The positive electrode is the positive electrode according to any one of claims 2 to 6,
The non-aqueous electrolyte secondary battery, wherein the one end is disposed on the outer peripheral side of the electrode group, and the other end is disposed in the center.   The non-aqueous electrolyte secondary battery according to claim 8, wherein in the electrode group, the first active material layer is disposed on the inner side and the second active material layer is disposed on the outer side.

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